According to the Uppsala Global Energy Systems(UGES) the total volume of crude oil consumed up to the year 2010 was about 1,100 Gb. If we add the remaining known reserves of crude oil to the amount that we expect the oil industry to find in the future then we also obtain a volume of 1,100 Gb. These figures differ greatly from reserve estimates provided by the 2013 BP Statistical Review 1668.9 Gb and other agencies like U.S. Energy Information Administration and the International Energy Agency.  
In 1984 the Middle Eastern members of OPEC reported reserves of 357Gb but by 1990 the reported reserves had increased to 644Gb which is a total increase of 80%. During that period no discoveries of new giant fields were reported despite the fact that many such discoveries would be required to give such an increase in reserves. By 2009 Middle Eastern members of OPEC had increased their reported reserves to 716Gb. Meanwhile during the last 20 years these nations have produced 143Gb. The question now is how large OPEC’s remaining reserves really are. (from pages 126 and 127 of “Peeking at Peak Oil”)
Three years later, OPEC member Venezuela doubled the size of its reserves by including the heavy oil from the Orinoco Belt which had not previously been counted. In response, the other OPEC nations increased the size of their reserves by the following amounts Abu Dhabi by 197%, Dubai by 186%, Iran by 90%, Iraq by 112%, and finally, Saudi Arabia by 51%. There is an area lying between Kuwait and Saudi Arabia that is called the “neutral zone” and is administered jointly by both nations. For that area no reserve increase was declared.
During the 1970’s the most influential members of the OPEC cartel had expropriated the assets of the international oil companies and transferred these to national oil companies. They also took possession of the technical data from the previous owners. Then, in 1985, Kuwait suddenly declared its reserves to be 40% larger than previously reported. The motivation behind this increase lies in how OPEC determines what volumes of oil its member nations are allowed to produce. Production volumes are determined partly on the basis of the size of a member nation’s oil reserves. When Kuwait increased its declared reserves it was able to increase its rate of oil production at the expense of the other OPEC nations production.

How much Oil is left?

Gb = 1 Billion Barrels

We consumed approximately 30Gb in 2010. UGES says we have about 1100 Gb left. The 2013 BPSR says there is about 1668.9 left. Let's assume that we continue into the future at the present rate of consumtion. This is not a projection because it won't happen like this, it is rather an illustration of the amount of Oil left.

1100 Gb divided by 30 equals 36.67 years left.

1668.9 Gb divided by 30 equals 55.63 years left.